JP4284604B2 - Contrast adjustment method and contrast adjustment apparatus for implementing the method - Google Patents

Description

  The present invention relates to a method, a program, and an apparatus for adjusting the contrast of a face area in a density characteristic curve used for density correction of captured image data including the face area.

  At present, in the photographic printing industry, it has been obtained by digitizing a photographed image data obtained by digitizing a photographed image formed on a photographic film using a film scanner or a digital photographing device such as a digital camera. After image processing such as density correction and color correction is performed on the photographed image data, it is converted into print data, and the print exposure unit is driven based on the print data to print the photographed image on a photosensitive material (printing paper). Digital photo processing technology is the mainstream.

  In the field of such digital photographic processing technology, for example, the image quality is determined based on R (red), G (green), and B (blue) photographed image data for each frame obtained by photometry of a photographic film with an image sensor. In order to print a good image on photographic paper, processing for correcting the density of the input captured image data is performed. As a density correction method, density correction based on a density characteristic curve (gamma characteristic) is generally used. In other words, the density gradation that the photographic paper develops does not match the density gradation of the input image data, so the density gradation that the photographic paper develops is set to be suitable for human visual characteristics. The input image data is corrected using the characteristic curve, and the density gradation that is colored on the photographic print (printing paper) that is finally obtained based on the corrected output image data corresponds to the human visual characteristics. I try to be something. As the density characteristic curve, a basic density characteristic curve created based on theoretical and empirical knowledge is well known, and such a basic density characteristic curve has been used for some time. However, the subject situation and the shooting environment situation of the shot image are various, and the basic density characteristic curve cannot obtain appropriate output image data depending on the shooting scene of the input shot image data. Has occurred. For example, when correcting photographic image data captured from photographic film taken with over / under exposure (overexposure / underexposure), the brightness of each pixel constituting the photographic image data is low (shadow) or high. The gradient of the shadow area and highlight area in the basic density characteristic curve is moderate, while the output density is extremely weak with respect to the input density. Will be corrected.

  In order to solve the above-described problem, the basic density characteristic curve is divided into a plurality of regions on the output side reference, and the range of input luminance that the basic density characteristic curve can take is changed with respect to the representative value of the image density. A data table that defines the adjustment rate is set for each area, a representative value of the density of the input image is obtained from the density of each pixel constituting the input image, and the representative value and the data table are used to obtain a representative value according to the input image. The adjustment rate according to the input image is adjusted to the input density range that can be taken by the basic density characteristic curve, while the output luminance range that can be taken by the reference gamma curve is constant for each area. Is applied to correct the basic density characteristic curve and correct the density of the input photographed image data with the corrected density characteristic curve (see Patent Document 1). By correcting the density using the corrected density characteristic curve as described above, the above-described problem can be improved to some extent. However, the effect is not sufficient for a specific photographed image, for example, a person photograph.

  In order to perform an appropriate density correction for a human photographed image, the feature amount of the RGB data of a pixel having a hue corresponding to the skin color of the person and the feature amount of the RGB data of a pixel in a region likely to include a person Some have been devised so that the density of a person is appropriately corrected by correcting the density characteristic curve based on the above (see Patent Document 2). Although this technique can improve a person-photographed image with a certain degree of probability, the skin color pixels do not uniquely define a person, so that an inappropriate density correction is performed depending on the subject.

  A technique is also known in which an operator designates a face area from captured image data and performs density correction based on the face area (see, for example, Patent Document 3 and Patent Document 4). When the basic density characteristic curve is corrected by adjusting the density so as to correct the density, overcorrection is often caused in a backlight photographed image or a flash photographed image, and an unnatural photo print is often produced.

  Also, the contrast is corrected by rotating the density characteristic curve around a predetermined point, generally around the point on the density characteristic curve that is the central density value (density histogram center). The same contrast correction is performed in the high density area and the low density area, and in particular, in the case of a backlit image or a strobe image, there is a problem that an image having satisfactory quality cannot always be created. . In order to solve this problem, the angle at which the density characteristic curve is rotated for contrast correction is changed by changing the angle at which the density characteristic curve is rotated on the high density side and the low density side, or the density characteristic curve is rotated for contrast correction. There is a technique for performing different contrast correction in a plurality of regions (for example, Patent Document 5). In such contrast correction, contrast correction for each density area is possible, but it is difficult to set the area that should be divided, that is, the density area that should be subjected to specific contrast correction, in person photographs, etc. It becomes contrast correction.

JP 2003-304398 A (paragraph numbers 0008 and 0021, FIG. 1) JP 2002-369020 A (paragraph number 0004-0008, FIG. 5) JP-A-6-59353 (paragraph numbers 0024 and 0048, FIG. 3) JP 2001-218047 A (paragraph numbers 0009-0010, 0024-0028, FIG. 2) JP 20021251130 (paragraph number 0094-0113, FIG. 4-5)

  In view of the above situation, an object of the present invention is to provide a contrast adjustment technique for appropriately adjusting the contrast of a face area in a density characteristic curve used for density correction of captured image data including the face area.

In order to solve the above problem, the contrast adjustment method according to the present invention, which adjusts the contrast of the face area in the density characteristic curve used for density correction of the captured image data including the face area, corrects the density of the captured image data including the face area. In the contrast adjustment method for adjusting the contrast of the face area in the density characteristic curve that defines the relationship between the input density and the output density used in the method, the step of detecting the face area from the photographed image data, and based on the photographed image data An appropriate density correction value that defines a shift amount for generating an appropriate density characteristic curve that is calculated and shifts a predetermined density characteristic curve parallel to the axis of the input density to realize correction suitable for the photographing data The output density value corresponding to the input density value of the specified density characteristic curve is neutral gray. Calculating and generating the proper density characteristic curve by shifting in parallel the predetermined density characteristic curve to the axis of the input density, the face average density value from the face region of the photographic image data, the A step of calculating a base density value which is a density value related to an unexposed portion of a photographic film of photographed image data or an optical black level, and a difference between the face average density value and the base density value is input. The face contrast coefficient indicating the slope of the density characteristic curve in the density value range of the pixels included in the face area is substituted by a predetermined function for calculating the contrast coefficient that defines the ratio between the density contrast and the output density contrast. calculating, in a straight line to tilt the face contrast coefficient within a predetermined density value, including the face average density value A step of determining, as face contrast, a straight line in which a corresponding output density value is a density value suitable for a face when the appropriate density correction value is set as an input density, and the input density value of the appropriate density characteristic curve is the predetermined density Generating an adjusted appropriate density characteristic curve for adjusting the contrast of the face area from the appropriate density characteristic curve by replacing the density range with the face contrast; and the captured image data based on the adjusted appropriate density characteristic curve And a step of performing density correction. In this method, with respect to an appropriate density characteristic curve determined based on photographed image data, the difference between the detected face average density value of the face area and the base density value of the photographed image data is used as a parameter. Since the face contrast coefficient indicating the slope of the characteristic curve is calculated and the face contrast determined by the appropriate density correction value that defines the face contrast coefficient and the appropriate density characteristic curve is combined with the appropriate density characteristic curve, the final appropriate density characteristic The curve has a contrast suitable for the face in the face area and a contrast suitable for a general subject in the other areas. The photographed image data that has been density-corrected and contrast-corrected using the appropriate density correction curve adjusted by this method can output a photographic print in which the density balance of the face area and background of the photographed image is appropriate. The proper density correction value that defines the proper density characteristic curve here is understood to be that a density value called neutral gray is output as the output density value when this appropriate density correction value is used as the input density value. May be. The base density value is generally the density value of the unexposed portion of the photographic film when the source of the photographed image data is a photographic film, and the optical black level when the source of the photographed image data is a digital camera or the like. Is a density value that is independent of the subject.

From the viewpoint of ease of processing, it is advantageous to adopt an area defined by the maximum density value and the minimum density value in the detected face area as the face area having the effective face contrast. Accordingly, in a preferred embodiment of the present invention, a step of calculating a face maximum density value and a face minimum density value from the captured image data of the face region is included, and the predetermined density is determined in the contrast determination step. range of values is in the range of the face minimum density value and the face maximum density value. In other words, when the input density value is within the range of the maximum face density value and the minimum face density value, the straight line with neutral gray as the output density value when the face contrast coefficient is the slope and the appropriate density correction value is the input density value is the face contrast. That is why.

  Instead of setting the area defined by the maximum face density value (maximum density value of the face area) and the minimum face density value (minimum density value of the face area) as the effective area of face contrast, the average face density (average density of the face area) An area separated from the (value) by a predetermined value may be set as the effective area. This predetermined value may be determined based on the density characteristic statistically obtained from the input captured image data, or may be set in advance.

  Various algorithms for determining the appropriate density characteristic curve and the appropriate density correction value are known. Here, in order to adapt to a human photograph, the appropriate density characteristic curve is based on the photographed image data. Between the basic density characteristic curve generated based on the basic correction value calculated in the above and the face-dependent density characteristic curve generated based on the average density value of the face area detected from the captured image data. An algorithm set so that the density characteristic curve is located is employed.

  The present invention also provides a program for causing a computer to execute the method for adjusting the contrast of the face area in the density characteristic curve used for density correction of the captured image data including the face area as described above, and a medium on which the program is recorded. It is the subject of rights.

In the present invention, the apparatus adopting the above-described method is also subject to the right, and the face area in the density characteristic curve that defines the relationship between the input density and the output density used for density correction of the captured image data including the face area. In the contrast adjustment device for adjusting the contrast of the image, a face detection unit for detecting a face area from the photographed image data and a predetermined density characteristic curve calculated based on the photographed image data are shifted in parallel with the input density axis . Thus, the output density value corresponding to the appropriate density correction value that defines the shift amount for generating the appropriate density characteristic curve that realizes the correction suitable for the photographing data is set as the input density value of the predetermined density characteristic curve. the proper concentration by shifting in parallel the predetermined density characteristic curve such but as a neutral gray to the axis of the input density An appropriate correction module that generates a sex curve, a face density calculation unit that calculates a face average density value from the face area of the photographed image data, and a blank portion of a photographic film that calculates a base density value of the photographed image data A base density calculation unit which is a density value or a density value related to the optical black level, and a difference between the face average density value and the base density value is defined as a ratio between an input density contrast and an output density contrast. A face contrast coefficient calculating unit that calculates a face contrast coefficient indicating a gradient of a density characteristic curve in a density value area of a pixel included in the face area by substituting into a predetermined function for calculating a contrast coefficient; and the face average density value corresponding to when the input density the appropriate density correction value of the straight line and the inclination of the face contrast coefficient within a predetermined density value including A face contrast determining unit that determines a straight line having an output density value suitable for the face as a face contrast, and replacing a range in which the input density value is the predetermined density in the appropriate density characteristic curve with the face contrast. A density characteristic curve determination module that generates an adjusted density characteristic curve for adjusting the contrast of the face area in the appropriate density characteristic curve, and a density correction unit that performs density correction of the captured image data based on the adjusted appropriate density characteristic curve And is composed of. Naturally, such a contrast adjustment device can obtain all the effects of the above-described method, and also uses the density characteristic curve adjusted by the contrast adjustment device to obtain photographic image data subjected to density correction and contrast correction. The photographic print based on this has good density balance and contrast balance in both the face area and background of the photographed image.

  It should be noted that the density characteristic curve or the density characteristic curve after contrast adjustment used here is not limited to a mathematical characteristic curve, but may be a discrete characteristic curve. Alternatively, it may be defined by a tabulated extractable data group often used in software, and input density is defined as output density in terms of software and / or hardware. This means all data structures that specify the density characteristics to be converted to.

An embodiment of a contrast adjustment technique according to the present invention will be described with reference to the drawings.
FIG. 1 is an external view showing a photographic printing apparatus incorporating a contrast adjustment technique according to the present invention. This photographic printing apparatus is a printing station 1B as a photographic printer that performs exposure processing and development processing on photographic paper P. FIG. And an operation station 1A that processes captured images taken from image input media such as developed photographic film 2a and digital camera memory card 2b, and generates / transfers print data to be used in print station 1B. Has been.

  This photo printing apparatus is also called a digital minilab, and as can be understood from FIG. The back print unit 13 prints print processing information such as color correction information and frame number on the back side of the photographic paper P, and the print exposure unit 14 cuts the print paper P into the size. A photographed image is exposed on the surface of the photographic paper P, and the exposed photographic paper P is sent to a processing tank unit 15 having a plurality of development processing tanks for development processing. After drying, the photographic paper P, that is, the photographic prints P, sent to the sorter 17 from the transverse feed conveyor 16 at the upper part of the apparatus is collected in a plurality of trays of the sorter 17 in a state of being sorted in order units (see FIG. 1). ).

  A photographic paper transport mechanism 18 is laid to transport the photographic paper P at a transport speed in accordance with various processes for the photographic paper P described above. The photographic paper transport mechanism 18 is composed of a plurality of nipping and transporting roller pairs including a chucker type photographic paper transport unit 18a disposed before and after the print exposure unit 14 in the photographic paper transport direction.

  The print exposure unit 14 applies R (red), G (green), and B (blue) to the printing paper P conveyed in the sub-scanning direction based on print data from the operation station 1A along the main scanning direction. A line exposure head for irradiating laser beams of the three primary colors (1) is provided. The processing tank unit 15 includes a color developing tank 15a for storing a color developing processing liquid, a bleach-fixing tank 15b for storing a bleach-fixing processing liquid, and a stabilizing tank 15c for storing a stable processing liquid.

  A film scanner 20 for obtaining photographed image data (hereinafter simply referred to as image data) from a photographed image frame of the photographic film 2a is disposed at the upper position of the desk-like console of the operation station 1A. A media reader 21 that acquires image data from various semiconductor memories, CD-Rs, and the like used as the photographed image recording medium 2b to be mounted is incorporated in a general-purpose personal computer that functions as the controller 3 of the photographic printing apparatus. The general-purpose personal computer is also connected with a monitor 23 for displaying various types of information, and a keyboard 24 and a mouse 25 as pointing devices used as operation input units used for various settings and adjustments.

  The controller 3 of this photographic printing apparatus uses a CPU as a core member and constructs a functional unit for performing various operations of the photographic printing apparatus by hardware and / or software, as shown in FIG. As described above, the functional unit particularly related to the present invention includes an image input unit 31 that takes in image data read by the scanner 20 and the media reader 21 and performs preprocessing necessary for the next processing, and various windows. And a graphic user interface (hereinafter abbreviated as GUI) for generating a control command from a user operation input (via the keyboard 24, mouse 25, etc.) through the graphic operation screen. The GUI unit 33 to be constructed and the control sent from the GUI unit 33 An image management unit 32 that performs image processing on the image data transferred from the image input unit 31 to the memory 30 in order to generate desired print data based on an operation command input from a command or a direct keyboard 24; A video control unit 35 that generates a video signal for causing the monitor 23 to display graphic data sent from the GUI unit 33, or a simulated image as a print source image, an expected finished print image, or the like during pre-judge printing work such as correction. A print data generation unit 36 that generates print data suitable for the print exposure unit 14 installed in the print station 1B based on the processed image data for which image processing has been completed, and a raw image according to customer requirements. Data and processed image data that have been processed Etc. formatter 37 for formatting into a form for writing in and the like.

  When the photographic image recording medium is the film 2a, the image input unit 31 separately sends the scan data for the pre-scan mode and the main scan mode to the memory 30, and performs preprocessing according to each purpose. When the captured image recording medium is the memory card 2b, when the captured image data includes thumbnail image data (low resolution data), the captured image is used for the purpose of displaying a list on the monitor 23. The thumbnail image data is sent to the memory 30 separately from the main data (high resolution data). If thumbnail image data is not included, a reduced image is created from the main data and sent to the memory 30 as low resolution image data.

  The image management unit 32 outputs a face detection unit 40 including face detection area data including face detection area data from a low resolution image data developed in the memory 30 using a face detection algorithm, and a high resolution developed in the memory 30. A density correction unit 50 that performs density correction on the image data, a density correction management unit 100 that sets and adjusts the density characteristic curve used by the density correction unit 50 based on the image characteristics of the image data, An image processing unit 200 that performs image processing such as filtering (such as blurring and sharpness) is provided.

  A general-purpose face detection unit 40 can be used. Here, based on a face detection algorithm, an area considered as a face in image data is detected, and the face position and size (the face position as a base point) are detected. Are used as face detection information including face detection area data, face orientation, and reliability calculated at the time of face detection. Many face detection algorithms for detecting a face from image data are known. For example, JP-A-11-339084, JP-A-2000-99722, and JP-A-2000-22929 are referred to. In addition, the face detection may be performed manually by an operator instead of automatically. In this case, the face detection unit 40 does not have a face detection algorithm and only outputs face detection information based on an operation input of the operator. It becomes the composition of.

  As shown in FIG. 4, the density correction unit 50 stores a density characteristic curve table 52 that stores an appropriate density characteristic curve that is set and adjusted by the density correction management unit 100 based on the image characteristics of the image data. Is used to perform density correction on high-resolution image data. Generally, the density correction unit 51 is realized by a program, and the density characteristic curve table 52 is realized by a data structure such as a look-up table. However, the present invention is not limited to this.

  Similarly, as shown in FIG. 4, the density correction management unit 100 is also realized by a program, and an appropriate correction module 60 that determines an appropriate correction value and a face contrast correction that determines the face contrast that is the contrast of the face area. The module 70 includes a density characteristic curve setting module 80 that generates an appropriate density correction curve based on the appropriate correction value and corrects the appropriate density correction curve based on the face contrast.

  As shown in FIG. 5, the proper correction module can be divided into a first correction submodule 60A and a second correction submodule 60B. The first correction submodule 60A includes a face detection evaluation unit 61, a face average density calculation unit 62, a face dependent density characteristic curve generation unit 63, a basic density characteristic curve generation unit 64, and a first correction value determination unit 65. The face detection evaluation unit 61 determines from the image information of the face area defined by the face detection information output from the face detection unit 40 whether the face is suitable for use in subsequent processing, If there are several faces that are determined to be suitable for the above, it has a sorting function to further reduce the number. The discrimination condition used at that time is the ratio of the skin color pixels in the face area and the reliability included in the face detection information, and the selection condition is the face position, size and orientation, the density of the face area, etc. It is done.

  The face average density calculation unit 62 calculates the average density value of the face area (single or plural) selected by the face detection evaluation unit 61, and the arithmetic average value of the R, G, B density values constituting each pixel. Further, it is calculated by arithmetically averaging the entire face area as an element.

  The basic density characteristic curve generation unit 64 positions a density characteristic curve having a predetermined reference characteristic (shape) on a coordinate plane based on the basic correction value on the coordinate plane with the input density on the horizontal axis and the output density on the vertical axis ( And has a function of generating a basic density characteristic curve. Note that even if the density characteristic curve is generated, generally, the density characteristic curve is not directly generated, but only a parameter for positioning the characteristic curve is calculated. This is also true for the generation of various density characteristic curves described later. That is, as is apparent from FIG. 6, when the basic correction value is used as the input density value, the density characteristic having the reference characteristic so that the output density value is neutral gray (95 × 256 for 16-bit data). A density characteristic curve generated by shifting the curve is a basic density characteristic curve. Various algorithms for calculating a basic correction value are known, but here, values obtained by multiple regression analysis are adopted using various image characteristics of input image data as explanatory variables.

  The face-dependent density characteristic curve generation unit 63 has a function similar to the basic density characteristic curve generation unit 64 described above, and here, the face average density value calculated by the face average density calculation unit 62 instead of the basic correction value. Is used. That is, as apparent from FIG. 7, when the face average density value is set as the input density value, the density value that is considered to express the face most beautifully is the output density value (160 × 256 in 16-bit data). Thus, the density characteristic curve generated by shifting the density characteristic curve having the reference characteristic becomes the face-dependent density characteristic curve.

In order to finish the face and the background other than the face in a well-balanced manner, the appropriate density characteristic curve that is actually used in the density correction unit 51 is an image to be processed between the basic density characteristic curve and the face-dependent density characteristic curve described above. It is important to set a position suitable for data density correction. For this reason, the first correction value determination unit 65 obtains a first difference value ΔD1 that is the difference between the basic density characteristic curve and the face-dependent density characteristic curve, and applies the first difference value ΔD1 to the next determination condition. First correction value: ε1 is determined (assuming that the density is expressed by 16-bit data);
(1) When ΔD1 <−6000, ε1 = v1 (negative number),
(2) When ΔD1> 12000, ε1 = v2 (positive number),
(3) When 0 <= ΔD1 <= 1000, ε1 = v3 (v1 << v3 << v2),
(4) In cases other than the above (1) to (3), ε1 = ΔD1 × 0.5.
The first difference value ΔD1 is represented by the difference between the input density values that give the same output density value, and may be obtained as an average difference between the two density characteristic curves over the entire area, or the face area. It may be obtained as an average difference between the two density characteristic songs over a range, or as a difference between the two density characteristic curves at a specific output value. Of course, a configuration may be adopted in which a plurality of subprograms for obtaining such a difference are prepared and selectively switched.

  When the density value obtained by adding the first correction value ε1 thus determined to the basic correction value is used as the input density value, the density characteristic curve setting module 80 outputs an output density value (95 for 16-bit data). The appropriate density characteristic curve used in the density correction unit 51 is generated by shifting the density characteristic curve so as to be a reference so that the standard density characteristic curve becomes × 256) (see FIG. 8).

However, when an appropriate density characteristic curve is set with the first correction value ε1, a photographed image with a small difference between the average density of the entire image and the average density of the face area tends to express the face area too much. In the embodiment, the final appropriate density characteristic curve is set by the second correction value ε2 determined in consideration of the average density value of the entire image in addition to the first correction value ε1. The second correction value is output by the second correction submodule 60B. For this reason, the second correction submodule 60B includes an image average density calculation unit 67 that calculates an image density value that is an average density value of pixels constituting the entire area of the low-resolution image data developed in the memory 30, and the second correction submodule 60B. A correction value determination unit 68 is provided. The second correction value determination unit 68 is a second difference value that is a difference between the face average density value calculated by the face average density calculation unit 62 and the image average density value calculated by the image average density calculation unit 67. Then, the adjustment rate is determined, and the second correction value ε2 is determined from the first correction value ε1 and the adjustment rate. At that time, using the second difference value ΔD2 and the first correction value ε1 (again, the density is expressed by 16-bit data), the adjustment rate ξ is determined from the following determination conditions;
(1) When (−3000 <= ΔD2 <−2000) and (ε1> = 0), ξ = w1,
(2) In the case of (−2000 <= ΔD2 <−1000) and (ε1> = 0), ξ = w2,
(3) When (−1000 <= ΔD2 <1000) and (ε1> = 0), ξ = w3,
(4) In the case of (1000 <= ΔD2 <2000) and (ε1> = 0), ξ = w4,
(5) When (2000 <= ΔD2 <3000) and (ε1> = 0), ξ = w5,
(6) When (−2000 <= ΔD2 <−1000) and (ε1 <0), ξ = w6,
(7) (−1000 <= ΔD2 <1000) and (ε1 <0) ξ = w7,
(8) When (1000 <= ΔD2 <2000) and (ε1 <0), ξ = w8,
(9) In cases other than (1) to (8) above, ξ = w9,
At that time the w1, w2, w3, w 4 , w5 are each a positive number a and w1 <w2 <w3, w5 < w4 <w3 exceeding 1.0, w6, w7, w8 is and a positive number less than 1.0 w7 <w8, w7 <w6, and w9 has a relationship of w1 <w9 <w7.
By multiplying the first correction value ε1 by the adjustment rate ξ determined in this way, the second correction value ε2 is obtained (ε2 = ε1 × ξ). When the density value obtained by adding the second correction value ε2 determined in this way to the basic correction value is used as the input density value, the density characteristic curve setting module 80 outputs an output density value that is neutral gray (95 for 16-bit data). The proper density characteristic curve used in the density correction unit 51 is generated by shifting the density characteristic curve so that it becomes a reference so that the standard density characteristic curve becomes × 256) (see FIG. 9). The density value obtained by adding the second correction value ε2 to the basic correction value is referred to as an appropriate correction value here.

  Next, the face contrast correction module for correcting the contrast of the face area in the appropriate density characteristic curve determined by the appropriate correction module 60 will be described. As shown in FIG. 10, the face contrast correction module 70 includes an average density value (face average density value) in a face area selected by the face detection evaluation unit 61 described above, preferably a skin color area in the face area. Based on the face density calculation unit 71 for calculating the maximum density value and the minimum density value, and the image base density which is the density value related to the film base density and the optical black level which is the density value of the blank portion of the photographic film. A base density calculation unit 72 that calculates the density; a face contrast coefficient calculation unit 73 that calculates a face contrast coefficient indicating the gradient of the density characteristic curve of the face region using the difference between the face average density value and the base density value as a parameter; The face contrast based on the density value, the minimum face density value, the face contrast coefficient, and the appropriate density correction value determined by the appropriate correction module 60. And a face contrast determining unit 74 for determining a. In this embodiment, since the face average density value is calculated by the face average density calculation unit 62 of the appropriate correction module 60, it can be used, or only the face average density value is calculated by the face average density calculation 62. It is also possible to omit the face density calculation unit 71 by calculating and storing the face maximum density value and the face minimum density value instead.

  In the face contrast coefficient calculation process in the face contrast coefficient calculation unit 73, as shown in FIG. 11, first, the base density (indicated by bD in the figure) and the face average density (indicated by fDave in the figure). ) (Concentration distance) a is obtained, and the contrast coefficient (slope) α is obtained by substituting the density distance a into the function f. This function f is used to obtain the contrast coefficient α using the density distance a as a parameter, and is obtained experimentally in advance. As implied in FIG. 11, the face contrast obtained in the following process is the minimum face density value (indicated by fDmin in the figure) and the maximum face density value (indicated by fDmax in the figure). One of innumerable straight lines having an inclination α in the region between.

  Next, in the process of determining the face contrast in the face contrast determination unit 74, as shown in FIG. 12, when the appropriate correction value determined by the appropriate correction module 60 is used as the input density, the output density value is the face most. Is determined to be a beautifully expressed density value of 160 × 256 (16-bit data), and within the infinite number of straight lines (see FIG. 11) defined by the face contrast coefficient calculation unit 73 A straight line passing through the point is specified, and this straight line is determined as the face contrast.

  The density characteristic curve determination module 80 adjusts the contrast of the face area by combining the determined face contrast with the appropriate density characteristic curve determined by the appropriate correction module 60, as schematically shown in FIG. A proper density characteristic curve is generated. That is, in the adjusted appropriate density characteristic curve, the part in the face area is replaced with the face contrast determined by the face contrast determination unit 74.

  A procedure for setting an appropriate density characteristic curve and correcting the contrast of the face area by the density correction management unit 100 configured as described above will be described. FIG. 14 shows a process for determining an appropriate density characteristic curve in the appropriate correction module 60. First, a basic density characteristic curve as shown in FIG. 6 is generated from the basic correction value obtained from the low resolution image data developed in the memory 30 using a multiple regression equation (# 01). At the same time, it is checked whether or not a face is detected from the face detection information output from the face detection unit 40 (# 02). If no face is detected (# 02 No branch), the basic density characteristic generated in step # 01 is checked. The curve is set in the density characteristic curve table 52 as an appropriate density characteristic curve used in the density correction unit 51 (# 03). If one or more faces are detected by the face detection unit 40 (# 02 Yes branch), based on the skin ratio that is the ratio of the number of skin color pixels to the number of face pixels calculated by referring to the face detection information. If necessary, a pre-selected face is selected from the pre-selected face based on the optimal ideal face obtained based on the face position and face size included in the face detection information. A selection process is performed in which only faces that fall within the divergence degree are selected for subsequent processing (# 04). The average density of the face area of the selected face, preferably the skin color area of the face area, is calculated as the face average density value (# 05). A face-dependent density characteristic curve as shown in FIG. 7 is generated from the calculated face average density value (# 06). A first difference value that is a difference between the face-dependent density characteristic curve and the basic density characteristic curve in the input density axis direction is obtained (# 07). The first correction value is determined from the first difference value using the above-described determination condition (# 08). An appropriate density characteristic curve as shown in FIG. 8 is generated using the first correction value (# 09).

  Next, the average density value of the entire image is calculated as the image average density value from the low resolution image data developed in the memory 30 (# 10). Subsequently, the difference between the image average density value and the face average density value calculated in step # 05 is calculated as a second difference value (# 11). Further, the second difference value and the first difference determined in step # 8 are calculated. The correction rate is determined from the correction value using the above-described determination condition (# 12). A second correction value is obtained by multiplying the first correction value and the correction rate (# 13). An appropriate density characteristic curve as shown in FIG. 8 is generated using the second correction value (# 14). Through the above processing, an appropriate correction value that is a density value obtained by adding the appropriate density characteristic curve and the second correction value ε2 to the basic correction value is obtained.

  FIG. 15 shows a contrast correction process in the face area of the appropriate density characteristic curve. First, the face average density value, the face maximum density value, and the face minimum density value are obtained (# 31), and the base density value is obtained (# 32). A density distance a which is a difference between the base density value and the face average density value is calculated (# 33). The contrast coefficient α is determined from the density distance value a using a function f (preferably configured as a look-up table) (# 34). An appropriate correction value is set (# 35). The face contrast is determined from the appropriate correction value, the face maximum density value, the face minimum density value, and the contrast coefficient acquired from the appropriate correction module 60 (see FIG. 12, # 36). The density characteristic curve setting module 80 generates a new appropriate density characteristic curve in which the contrast of the face area is corrected from the face contrast output from the face contrast correction module 70 and the appropriate density characteristic curve output from the appropriate correction module 60. (See FIG. 13, # 37). The proper density characteristic curve finally generated in this way is set in the density characteristic curve table 52 (# 38). Through the above procedure, the density characteristic curve table 52 has been set with the optimum density characteristic curve for the low resolution image data including the face developed in the memory 30. Density correction processing is performed on the corresponding high-resolution image data developed in the memory 3. As a result, the contrast of the face area of the high-resolution image data used for printing is optimally adjusted, and as a result, a photographic print that expresses the face beautifully can be output.

  In the above-described embodiment, the print station 1B exposes a photographed image to the photographic paper P by the print exposure unit 14 having an exposure engine, and performs a plurality of development processes on the photographic paper P after the exposure. Although the silver salt photographic printing method was adopted, of course, the printing station 1B according to the present invention is not limited to such a method. For example, an ink jet that ejects ink onto a film or paper to form an image. Various photographic printing methods such as a printing method and a thermal transfer method using a thermal transfer sheet can be employed.

  The present invention relates to a technical field for generating a density characteristic curve in which the contrast of a face area is optimally adjusted by using face image characteristics detected from photographed image data, and more particularly to a photographic print for creating a photographic print from photographed image data It can be widely used as a contrast adjustment module incorporated in the apparatus.

External view of photographic printing apparatus employing density correction management technology according to the present invention Schematic diagram schematically showing the configuration of the print station of the photo printing device Functional block diagram explaining the functional elements built in the controller of the photo printing device Functional block diagram showing the functional configuration of the density correction correction management unit Functional block diagram showing the functional configuration of the appropriate correction module Schematic diagram explaining generation of basic density characteristic curve Schematic diagram explaining generation of face-dependent density characteristic curve Schematic diagram for explaining generation of an appropriate density characteristic curve in the first embodiment of the density correction management unit. Schematic diagram illustrating generation of an appropriate density characteristic curve in the second embodiment of the density correction management unit Functional block diagram showing the functional configuration of the face contrast correction module Schematic diagram explaining the contrast coefficient calculation procedure Schematic diagram explaining the procedure for determining the face contrast Schematic diagram for generating an appropriate density characteristic curve with corrected face contrast in the face area Flow chart showing the flow of processing for generating an appropriate density characteristic curve The flowchart which shows the flow of the process which produces | generates the appropriate density characteristic curve by which the face contrast in the face area | region was corrected

Explanation of symbols

30: Memory 40: Face detection unit 50: Density correction unit 51: Density correction unit 52: Density characteristic curve table 60: Appropriate correction module 60A: First correction submodule 60B: Second correction submodule 61: Face detection evaluation unit 62 : Face average density calculation unit 63: face dependent density characteristic curve generation unit 64: basic density characteristic curve generation unit 65: first correction value determination unit 67: image average density calculation unit 68: second correction value determination unit 70: face contrast Correction module 71: Face density calculation unit 72: Base density calculation unit 73: Face contrast coefficient calculation unit 74: Face contrast determination unit 80: Density characteristic curve setting module 100: Density correction management unit 200: Image processing unit

Claims (4)

In a contrast adjustment method for adjusting the contrast of a face area in a density characteristic curve that defines the relationship between input density and output density used for density correction of captured image data including a face area,
Detecting a face region from the captured image data;
A shift amount for generating an appropriate density characteristic curve that is calculated based on the photographed image data and realizes correction suitable for the photographed data by shifting a predetermined density characteristic curve parallel to the axis of input density is defined. By shifting the predetermined density characteristic curve in parallel with the input density axis so that the corresponding output density value becomes neutral gray when the appropriate density correction value to be used is the input density value of the predetermined density characteristic curve. Generating the appropriate density characteristic curve;
Calculating a face average density value from the face area of the captured image data;
Calculating a base density value, which is a density value related to an optical black level or a density value of a blank portion of the photographic film of the photographed image data;
By substituting the difference between the face average density value and the base density value into a predetermined function for calculating a contrast coefficient that defines the ratio between the contrast of the input density and the contrast of the output density, the pixels included in the face area Calculating a face contrast coefficient indicating the slope of the density characteristic curve in the density value range;
Of the straight lines having the face contrast coefficient as a slope within the range of the predetermined density value including the face average density value, the output density value corresponding to the input density as the appropriate density correction value is a density value suitable for the face. Determining a straight line as face contrast;
Generating an adjusted appropriate density characteristic curve for adjusting the contrast of the face area from the appropriate density characteristic curve by replacing the range of the predetermined density of the appropriate density characteristic curve within the predetermined density with the face contrast; ,
And a step of correcting the density of the photographed image data based on the appropriate adjustment density characteristic curve.   A step of calculating a face maximum density value and a face minimum density value from the captured image data of the face area, and in the contrast determining step, the range of the predetermined density value is the face maximum density value and the face minimum density The contrast adjustment method according to claim 1, wherein the contrast adjustment method is in a range of values.   The program for making a computer perform the contrast adjustment method of the said Claims 1-2. In a contrast adjustment device that adjusts the contrast of a face area in a density characteristic curve that defines the relationship between input density and output density used for density correction of captured image data including a face area,
A face detection unit for detecting a face area from the captured image data;
A shift amount for generating an appropriate density characteristic curve that is calculated based on the photographed image data and realizes correction suitable for the photographed data by shifting a predetermined density characteristic curve parallel to the axis of input density is defined. By shifting the predetermined density characteristic curve in parallel with the input density axis so that the corresponding output density value becomes neutral gray when the appropriate density correction value to be used is the input density value of the predetermined density characteristic curve. An appropriate correction module for generating the appropriate density characteristic curve;
A face density calculation unit that calculates a face average density value from the face area of the captured image data;
A base density calculation unit that is a density value related to an optical black level or a density value of a blank portion of a photographic film that calculates a base density value of the photographed image data;
By substituting the difference between the face average density value and the base density value into a predetermined function for calculating a contrast coefficient that defines the ratio between the contrast of the input density and the contrast of the output density, the pixels included in the face area A face contrast coefficient calculating unit for calculating a face contrast coefficient indicating the slope of the density characteristic curve in the density value range;
Of the straight lines having the face contrast coefficient as a slope within the range of the predetermined density value including the face average density value, the output density value corresponding to the input density as the appropriate density correction value is a density value suitable for the face. A face contrast determination unit that determines a straight line as the face contrast;
A density characteristic curve that generates an adjusted density characteristic curve for adjusting the contrast of the face area in the appropriate density characteristic curve by replacing the range of the predetermined density of the appropriate density characteristic curve within the predetermined density with the face contrast. A decision module;
A density correction unit that performs density correction of the captured image data based on the adjustment appropriate density characteristic curve;
A contrast adjusting device characterized by comprising:

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